1. Field of the Invention
The present invention relates to a radio telecommunication apparatus such as a pager receiver having a function of receiving transmission information transmitted from an information source via a radio channel and displaying the received information on a display.
2. Description of the Related Art
In recent years, a system in which message information is transmitted from a base station and displayed by a pager receiver has been developed as an advanced paging system. A paging signal used in the paging system of this type has, e.g., a format as shown in FIG. 1. That is, one frame is time-divided into a plurality of groups (n groups), and each group is time-divided into a preamble word and a plurality of calling words (m words). An ID code and a message code are inserted in each calling word.
In order to call a pager receiver, a caller dials a telephone number corresponding to the pager receiver to call a base station and sends message information to the base station. The base station generates a predetermined ID code corresponding to the pager receiver and a message code obtained by encoding the message information. The ID code and the message code are inserted in an empty calling word in a group of a plurality of groups of one frame, to which the pager receiver belongs, and are transmitted.
The pager receiver has, e.g., the following arrangement. That is, the paging signal transmitted from the base station is received by a radio circuit via an antenna, demodulated by a demodulation circuit and input to a controller. The controller collates the ID code included in the demodulated paging signal with its own ID code stored in an ID-ROM beforehand. If a coincidence is detected between the two codes upon collation, it is determined that a call is generated to its own receiver, and a ringing signal is output. This ringing signal is supplied to a speaker via a driver. Therefore, the speaker generates a ringing tone to alarm generation of the call to the owner of the receiver.
If the coincidence between the ID codes is detected, the controller performs error correction processing for the message code received subsequently to the ID code and decodes the processed code. The decoded message data is supplied from the controller to a display driver. Therefore, the message is displayed on a liquid crystal display (LCD) by the display driver. In this manner, if a call is generated, an owner of the receiver can know the message from a caller by seeing the liquid crystal display.
Recently, as an advanced information transmission system using a paging system of this type, a system in which service information such as a foreign exchange rate or a stock price is transmitted from an information source to a specific pager receiver has been developed. In a system of this type, a pager receiver requiring reception of the service information is assigned with a second ID code different from the first ID code used to perform normal calling described above. This second ID code is commonly given to all pager receivers requiring reception of the service information. In order to transmit the service information, a source of the service information calls the base station and transmits the service information. The base station generates the second ID code and a service code obtained by encoding the service information. These codes are inserted in an empty calling word of each of all groups of the paging signal and are transmitted to the pager receivers.
Each pager receiver requiring reception of the service information performs collation for the first and second ID codes. If the second ID code is detected, the service code received together with the second ID code is decoded by the controller and supplied to the display driver. The service information is displayed on the liquid crystal display. Therefore, an owner of the receiver can check the contents of the service information by seeing the display.
This system, however, has the following problems. That is, if a calling word including service information is received, the pager receiver generates, e.g., a ringing tone to alarm reception of the service information to the owner of the receiver. It becomes difficult, however, for the owner to distinguish normal calling from reception of the service information. In addition, even if service information not so important for an owner is received, a ringing tone or the like is always generated to alarm the reception to the owner. Therefore, the owner must perform an operation for stopping the ringing tone each time the ringing tone is generated, resulting in very cumbersome operation.
In order to facilitate distinguishment between normal calling and reception of service information, the arrangement may be modified such that no ringing tone is generated when the service information is received. In this case, however, the owner of the receiver may often be unaware of reception of the service information. Therefore, if a check on the service information is delayed, the owner may not be able to immediately cope with, e.g., a sudden drop in stock price or a rapid change in exchange rate.